The present invention relates to flexible electrostatographic imaging belt members and, more specifically, to imaging belts having mechanically robust outer exposed layers that possess, for example, anti-curl backing layers or ground strip layers with enhanced wear resistance and optical transparency properties.
Flexible electrophotographic imaging members are well known in the art. Typical electrostatographic flexible imaging members include, for example, photosensitive members, such as photoreceptors, commonly utilized in electrophotographic, such as xerographic processes and electroreceptors, and ionographic imaging members for electrographic imaging systems. The flexible electrostatographic imaging members may be seamless or seamed belts. Typical electrophotographic imaging member belts comprise an imaging layer which is a charge transport layer and a charge generating layer on one side of a supporting substrate layer and an anti-curl backing layer coated on the opposite side of the substrate layer. A typical electrographic imaging member belt comprises a dielectric imaging layer on one side of a supporting substrate and an anti-curl backing layer on the opposite side of the substrate. A typical flexible electrostatographic imaging member belt has a ground strip coated near one edge of the belt and adjacent to the imaging layer.
Flexible electrophotographic imaging belt members may comprise a photoconductive layer comprising a single layer or composite layers. One type of composite photoconductive layer used in electrophotography is illustrated in U.S. Pat. No. 4,265,990, which describes a photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, where the two electrically operative layers are supported on a conductive layer with the photoconductive layer sandwiched between the contiguous charge transport layer and the conductive layer, the outer surface of the charge transport layer is normally charged with a uniform charge of a negative polarity and the supporting electrode is utilized as an anode. The supporting electrode may still function as an anode when the charge transport layer is sandwiched between the supporting electrode and the photoconductive layer. The charge transport layer in this latter embodiment must be capable of supporting the injection of photogenerated electrons from the photoconductive layer and transporting the electrons through the charge transport layer. Photosensitive members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged with a uniform negative electrostatic charge, exposed to a light image and then developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For electrophotographic imaging members having a belt configuration, the numerous layers found in modem photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multi-layered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer, and a conductive ground strip layer adjacent to one edge of the imaging layers. This photoreceptor belt may also comprise additional layers such as an anti-curl backing layer to achieve the desired belt flatness. An optional overcoating layer over the charge transport layer may be used for additional wear, environmental, and chemical protection.
In a machine service environment, a flexible imaging member belt, mounted on a belt supporting module, is generally exposed to repetitive electrophotographic image cycling which subjects the exposed anti-curl backing layer to abrasion due to mechanical fatigue and interaction with the belt drives and other support rollers as well as sliding contact with backer bars. This repetitive cycling leads to a gradual deterioration in the physical/mechanical integrity of the exposed anti-curl backing layer. When the anti-curl layer is worn the thickness thereof is reduced and the anti-curl backing layer experiences a loss of ability to counteract the tendency of imaging members to curl upwardly thereby leading to belt curl. Moreover, uneven wear of the anti-curl backing layer has been found to cause early development of belt ripples which are ultimately manifested as copy printout defects. Thus, the anti-curl backing layer wear that results from mechanical contact interaction during dynamic imaging operations is a significant problem that shortens the service life of the belt and adversely affects image quality.
When a production web stock of several thousand feet of coated multi-layered photoreceptor is rolled up, the charge transport layer and the anti-curl layer are in intimate contact. The high surface contact friction of the charge transport layer against the anti-curl layer causes dimples and creases to develop in the internal layers of the photoreceptor. Since these physically induced defects manifest themselves as print defects in xerographic copies, the unacceptable segments of this photoreceptor web stock are discarded thereby decreasing production yield. Although attempts have been made to overcome these problems, the solution of one problem often leads to the generation of additional problems.
Flexible photoreceptor belts are fabricated from sheets cut from an electrophotographic imaging member web stock. The cut sheets are generally rectangular in shape. All edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheet is formed into a belt by joining the overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping opposite marginal end regions at the point of joining. Joining may be effected in any suitable manner, such as welding including for example ultrasonic processes, gluing, taping, pressure/heat fusing, and the like methods. However, ultrasonic seam welding is generally the preferred method of joining because it is rapid, clean, generally free of solvent application, and produces a thin and narrow seam. The ultrasonic seam welding process involves a mechanical pounding action of a welding horn which generate a sufficient amount of heat energy at the contiguous overlapping marginal end regions of the imaging member sheet to maximize melting of one or more layers therein. A typical ultrasonic welding process is carried out by holding down the overlapping ends of the flexible imaging member sheet with vacuum onto a flat anvil and guiding the flat end of the ultrasonic vibrating horn transversely across the width of the sheet and directly over the overlapped junction to form a welded seam having two adjacent seam splashings consisting of the molten mass of the imaging member layers ejected to the either side of the welded overlapped seam. These seam splashings of the ejected molten mass comprise about 40 percent by weight of anti-curl layer material. The splashings can include hard crystalline materials and have a rough abrasive outer surface which abrades the photoreceptor cleaning blade during dynamic image cycling causing the blade to lose cleaning efficiency and shortens blade service life.
Alteration of material formulation in the anti-curl backing layer of imaging member belt can enhance wear resistance and extend life, but this enhancement can lead to certain undesirable outcomes. For example, incorporation of crystalline particles in the outermost exposed layers of the imaging member to improve wear resistance has been observed to cause excessive wear of the ultrasonic horn used to ultrasonically weld the seams of imaging belts. Other prior art approaches, reference for example, U.S. Pat. Nos. 5,096,795 and 5,725,983, demonstrate that to resolve imaging member coating layer wear problems, synthetic organic particles as well as blends of organic and inorganic particle dispersions can be incorporated into the exposed anti-curl backing layer of the imaging member and can thereby improve abrasion resistance. However, such incorporation often caused bubble formation in the dried anti-curl backing layer. These bubbles adversely affect the thickness uniformity of the layer which in turn affects critical physical characteristics such as, for example, alteration of intimate surface contact friction requirements between the anti-curl backing layer and the drive-roller of the belt support module. This alteration of friction adversely impacts the driving capacity of drive-rollers and causes imaging belt slippage during dynamic belt operation. Moreover, the alteration has also been found to reduce the mechanical strength of anti-curl backing layers and capability to resist fatigue induced anti-curl backing layer cracking. The presence of bubbles in the anti-curl backing layer can also negate and diminish the benefit of wear resistance enhancements that are otherwise achievable through dispersion of organic particles in imaging members by, for example, increasing wear rate. Also the presence of bubbles can weaken the layer and cause premature cracking of the imaging member when fatigue tension/compression strain is repeatedly applied to the anti-curl backing layer during machine cycling, particularly during fatigue cycling around small diameter support rollers. Further, when rear or back erase is employed to discharge the photoreceptor belt during electrophotographic imaging processes, the presence of bubbles can cause light scattering which can lead to undesirable non-uniform discharge of the imaging member. Also, the presence of bubbles in the anti-curl backing layer during seam welding processes cause the bubbles to expand and form splashings having open pits. During electrophotographic imaging and cleaning cycles, these open pits can function as sites that trap toner, debris, and dirt particles making attempts to clean the imaging member belt extremely difficult. It has also been found that, during imaging belt cycling, the trapped toner, debris, and dirt particles can be carried out by the cleaning blade from the pits to contaminate vital imaging componentry, such as lenses, Hybrid Scavengeless Development (HSD), Hybrid Jumping Development (HJD), and other subsystems, and can also lead to undesirable artifacts which form undesirable print defects in the final image copies. An additional shortcomings of organic and inorganic fillers dispersion in the outer exposed anti-curl backing layer include the creation of surface protrusions, that is particulate filler materials which extend beyond the boundaries of the coating film layer. Protrusions can diminish the optical clarity of the resulting layer and interfere, for example, with efficient back erase discharge.
A flexible electrophotographic imaging belt member's ground strip is typically coated adjacent to the charge transport layer and is also an outer exposed layer. The ground strip layer is constantly subjected to mechanical action by, for example, static grounding devices or the sliding motion of cleaning blades during xerographic imaging or cleaning processes. Premature ground strip wear-through has been identified as a problem which requires immediate replacement of the belt. A ground strip wear-through site not only can disrupt electrical conductivity, the wear-through site also functions like an aberrant timing hole which can generate faulty belt cycling registration signals.
There remains a need for simple and efficient method for improving the shortcomings of the abovementioned anti-curl backing layers and ground strip layers in electrostatographic imaging belt members. In embodiments, the imaging member articles and apparatus of present invention provide unexpected benefits and superior productivity performance levels in electrostatographic imaging processes. These and other advantages of the present invention are illustrated herein.